1. Field of the Invention
The present invention relates to an electronic circuit unit and a method of fabricating the same, for use in a local area wireless apparatus.
2. Description of the Related Art
With respect to a conventional electronic circuit unit and a method of fabricating the same, FIG. 8 is a cross-sectional view showing principal parts of the conventional electronic circuit unit, and FIG. 9 is an explanatory view illustrating the method of fabricating the conventional electronic circuit unit.
Next, an arrangement of the conventional electronic circuit unit will be described with reference to FIGS. 8 and 9. Wiring patterns 52 are formed on the front surface and the rear surface of a circuit board 51 which is composed of a plurality of stacked insulating sheets. In addition, a solder resist film 53 land units 52b and electrodes 52a exposed from the solder resist film 53 are formed on the wiring pattern 52.
With the solder resist film 53, regions of the electrodes 52a and the land units 52b are formed, and the wiring patterns 52 other than the exposed electrodes 52a and land unit 52b are prevented from being broken. In addition, since the solder resist film 53 is formed through printing or deposition of liquefied insulating material, the thickness of a film is not uniform such that an uneven film is formed.
Thus, on the front surface of the circuit board 51, bumps 55 arranged on a semiconductor chip 54 are pressed on the electrodes 52, and the semiconductor chip 54 is mounted on the circuit board 51 while chip parts 56 are soldered to the land unit 52b. In addition, on the rear surface of the circuit board 51, chip parts 57 are soldered to the land units 52 to form a desired electric circuit, so that the conventional electronic circuit unit is fabricated (See Japanese Unexamined Patent Application Publication No. 2000-307212).
A method of fabricating the conventional electronic circuit unit having the above-mentioned arrangement will be described with reference to FIG. 9. First, the solder resist film 53 to be formed on both sides of circuit board 51 is prepared. Next, as shown in FIG. 1, the solder resist film 53 on the rear surface of the circuit board 51 is placed on the supporting jig 61.
Here, since the thick film of the solder resist film 53 arranged on the back of the circuit board 51 is uneven, the circuit board 51 is supported such that the circuit board 51 is tilted against the surface of the supporting jig 61.
Next, the semiconductor chip 54 is carried onto the electrodes 52a through a mounting jig 62 for absorption and pressing, and the bumps 55 are heated and pressed down to the electrodes 52a by the mounting jig 62. Thus, the bumps 55 are adhered to the electrodes 52a, and then, the mounting jig 62 return to its original position.
In addition, the pressing of the bumps 55 to the electrodes 52a is performed while being tilted against the circuit board 51, such that some bumps are not sufficiently adhered to the electrodes 52a. As a result, the semiconductor chip 54 is not sufficiently mounted which leads to an unreliable mounting capability.
Therefore, after the semiconductor chip 54 is mounted, first, the chip parts 56 are soldered to the land unit 52b by using cream soldering arranged on the land units 52b. Next, the chip parts 57 are soldered to the land unit 52b by using cream soldering arranged on the land unit 52b to complete the fabrication process.
Specifically, according to the conventional electronic circuit unit and the method of fabricating the same, since the solder resist film 53 exists on the rear side of the circuit board 51, the circuit board 51 is tilted due to the unevenness of the thickness of the solder resist film 53 during the mount process of the semiconductor chip 54. As a result, the semiconductor chip 54 is not sufficiently mounted which leads to an unreliable mounting.
In the conventional electronic circuit unit and the method of fabricating the same, there is a problem in that, since the solder resist film 53 exists on the rear side of the circuit board 51, the circuit board 51 is tilted due to the unevenness of the thickness of the solder resist film 53 during the mount process of the semiconductor chip 54. As a result, the semiconductor chip 54 is not sufficiently mounted which reads to an unreliable mounting.